Technical Abstract:
Wild strawberry species exhibit a range of breeding systems including hermaphroditism, dioecy, and gynodioecy. Breeders of cultivated strawberry, Fragaria ×ananassa Duchesne ex Rozier, prefer self-pollinating hermaphrodites, but major sources of pest resistance are the wild octoploid progenitor species, F. virginiana Mill. and F. chiloensis (L.) Mill, which are sexually dimorphic. Therefore, a program that can isolate genomic regions controlling sex expression from other desirable traits may facilitate strawberry breeding and further our understanding of sex expression. To identify regions controlling sex expression in Fragaria L., we developed a mapping population from a cross between a female and a low-fruiting hermaphrodite, both F. virginiana. At each of two locations (greenhouse and field), we grew three clones each of 184 progeny, scored individuals both qualitatively with respect to male or female fertility (i.e., sex type) and quantitatively with respect to primary sexual traits including fruit set, flower number, ovule, anther, and pollen number per flower, and pollen viability. To construct a genetic map, we screened several hundred SSR primer pairs for polymorphisms. Preliminary results reveal 52 linkage groups, including both coupling and repulsion phases. Male sterility mapped to a single linkage group with very strong association to at least one marker. These results are promising for the development of marker-assisted strawberry breeding programs that include wild strawberry enhancement. We will use this map further to identify genomic regions associated with the quantitative measures of sex expression.